Machining spur sprocket to accept rim

[vrex]

Hopefully this is the right place for my question, searching for this has been tricky in trying to figure out the keywords that return results. I was speaking with @Ketchup about converting an echo 2511/2500 to .325 (or 1/4p if thats what it comes down to). Yes, spur sprockets exist for these saws, i have the part numbers, but Echo isnt making it easy to access them. I saw the group buy on them, but im wondering: what does it take to machine a spur (paddle style) sprocket down to accept a rim drive? I'm no machinist, just a beer drinker, so I understand turning down teeth to match the ID of the rim, but then how do you get splines to retain and drive the rim? Has this been done? Can it be done? I'm interested in a solution that doesnt cost 1/4 the price of the saw for a part from the UK. I'd happily send off 2 echo 3/8 spurs for my 2500t (new acquisition, its been awesome in the tree for everything except removals) to have them machined and then be able to try out husky sp21 on the saw or failing that 1/4p (trying to avoid 1/4p and i rather like sp21g as we use it at our tree service on the t540iXP and it performs damn fine). What do the machining wizards know about this?

 

[davidwyby]

Got a pic of the spur?

 

[wcorey]

I'd say it would be easier to machine the spline part from scratch and weld it to a 2511 drum with the spur removed. Easier being a relative term...

Or better still...
Remove a rim spline from another drum and weld it the the donor 2511 drum.

Can't imagine either option being cost effective to have done professionally.

 

[vrex]

Well if the cost is going to be more than or equal to, guess I’m SOL on my idea. When I’m home I’ll get pics of the sprocket up, along with some measurements but I‘d venture the cost:benefit is out off whack here. Thank you!

 

[Nutball]

srcarr52 was telling me something about how hard it would be to weld those kinds of metal or retaining the appropriate hardness or something, and he should know.

 

[vrex]

srcarr52 was telling me something about how hard it would be to weld those kinds of metal or retaining the appropriate hardness or something, and he should know.

I do believe @srcarr52 counts as a wizard haha

 

[davidwyby]

Machine shop $125/hr. Gotta do a bunch of anything to make it economically viable.

 

[davidwyby]

https://www.amickssuperstore.com/Echo_1_4_Sprocket_CS_2511T_p/ami001710.htm

 

[srcarr52]

srcarr52 was telling me something about how hard it would be to weld those kinds of metal or retaining the appropriate hardness or something, and he should know.

They'd be super prone to cracking at the heat effected zone of the welds. This is why they are brazed.

Also, those spurs are pretty hardened, I would venture to say machining them would be a pain. Maybe it could be done with a 4 axis where your can get the root radius of the spline perpendicularly with larger tooling. But profiling them would be out as you couldn't make the spline shoulder and broaching something that hard is out of the question.

 

[vrex]

https://www.amickssuperstore.com/Echo_1_4_Sprocket_CS_2511T_p/ami001710.htm

Thank you, unfortunately the 2511t spur doesnt fit the 2500t, different should sitting on the PTO side, two flats on the 2500t retain and drive it vice the 2511t's spline. If only echo was smart enough to just use the same part seeing as its already in their system, engineered and works fine... can't fix stupid

 

[vrex]

They'd be super prone to cracking at the heat effected zone of the welds. This is why they are brazed.

Also, those spurs are pretty hardened, I would venture to say machining them would be a pain. Maybe it could be done with a 4 axis where your can get the root radius of the spline perpendicularly with larger tooling. But profiling them would be out as you couldn't make the spline shoulder and broaching something that hard is out of the question.

I figured between the ability of the thing to take heat, and how much actual working material would be left to cut shoulders for the splines, you'd need a CNC, and that means cost. Do you feel like the spurs could be turned down to a simple cylinder, the rim drive harvested from another clutch drum and have that machined out enough for an interference fit? Hopefully I'm articulating that well enough to be understood...

 

[srcarr52]

I figured between the ability of the thing to take heat, and how much actual working material would be left to cut shoulders for the splines, you'd need a CNC, and that means cost. Do you feel like the spurs could be turned down to a simple cylinder, the rim drive harvested from another clutch drum and have that machined out enough for an interference fit? Hopefully I'm articulating that well enough to be understood...

Rim drives need to float on the splines to line up with the bar groove.

 

[Nutball]

A soft adapter could be made between the OD of the turned down sprocket and the ID of the rim. The adapter could get heat treated after being made. Hard metal is easy enough to machine with big cutters.

 

[Shane¹]

What is so special about this drum is it an odd size? There is not a drum off a different saw that would fit?

 

[davidwyby]

Drum a lot easier to mod than rim/spline. Maching splines up agains the drum no go. Waterjet splined hub or rob from other drum, weld to turned down spur...hardness is issue as stated. Maybe remove entire spur from drum for new or scavenged spline drive.

My 6100 is small spline. I thought about waterjetting adapters from small to large.

 

[Maintenance Chief]

Bill G. On the other site had pictures of a spur drive modified to receive a spline rim . Theoretically you only have to do it once as the rim is replaceable.

 

[vrex]

What is so special about this drum is it an odd size? There is not a drum off a different saw that would fit?

Its for an electric top handle, echo's 2500t. No clutch, just two flats. I dont know enough about what other saws might possibly have a similar arrangement, but I'm all ears if anyone knows. Let me know what info i can provide off my spur to assist, thank you!

 

[vrex]

spur/drum dimensions and oiler setup

 

[vrex]

drum ID

 

[wcorey]

Do you feel like the spurs could be turned down to a simple cylinder, the rim drive harvested from another clutch drum and have that machined out enough for an interference fit? Hopefully I'm articulating that well enough to be understood...

I didn't read into your original post enough to realize this is for a battery saw and subsequently how it's attached to the saw. Looks like the drum is just there for the brake and dust shield for the oil pump.
Assuming you mean harvesting the splined hub from a drum, then yes, I think that could be done, with the motor drive shaft being just 10mm and no clutch bearing it leaves some room to play with. An interference fit alone would be pushing it though, brazing it on would be easy enough but then you have to deal with re-heat treating which is potentially problematic not knowing what the metallurgy is.